Human stem cells are totipotential or pluripotential precursor cells capable of generating a variety of mature human cell lineages. Evidence exists that demonstrates that stem cells can be employed to repopulate many, if not all, tissues and restore physiologic and anatomic functionality.
Many different types of mammalian stem cells have been characterized. See, e.g., Caplan et al., U.S. Pat. No. 5,486,359 (human mesenchymal stem cells); Boyse et al., U.S. Pat. No. 5,004,681 (fetal and neonatal hematopoietic stem and progenitor cells); Boyse et al., U.S. Pat. No. 5,192,553 (same); Beltrami et al., Cell 114(6):763-766 (2003) (cardiac stem cells); Forbes et al., J. Pathol. 197(4):510-518 (2002) (hepatic stem cells). Umbilical cord blood, and total nucleated cells derived from cord blood, have been used in transplants to restore, partially or fully, hematopoietic function in patients who have undergone ablative therapy.
The placenta is a particularly attractive source of stem cells. Because mammalian placentas are plentiful and are normally discarded as medical waste, they represent a unique source of medically-useful stem cells.
Bone marrow-derived mesenchymal stem cells have recently been shown, when genetically modified, to have the ability to migrate into, and infiltrate, certain tumor cells. See, e.g., Hung et al., “Mesenchymal Stem Cell Targeting of Microscopic Tumors and Tumor Stroma Development Monitored by Noninvasive In vivo Positron Emission tomography Imaging,” Clin. Cancer Res. 11(21):7749-7756 (2005). Certain genetically engineered bone marrow-derived mesenchymal stem cell lines have been shown to suppress tumor growth. See, e.g., Studney et al., “Bone Marrow-derived Mesenchymal Stem Cells as Vehicles for Interferon-β Delivery into Tumors,” Cancer Res. 62:3603-3608 (2002) (melanoma cell line); Nakamura et al., “Antitumor Effect of Genetically Engineered Mesenchymal Stem Cells in a Rat Glioma Model,” Gene Therapy 11:1155-1164 (2004 (mesenchymal stem cells expressed recombinant IL-2). Mesenchymal stem cells, however, have been shown to promote the growth of at least one kind of tumor in vivo. See Zhu et al., “Mesenchymal Stem Cells Derived from Bone Marrow Favor Tumor Cell Growth In Vivo,” Exp. Mol. Pathol. (epublication prior to publication, 2005) (colon adenocarcinoma cells).
To date, however, no one has described the ability of placenta-derived stem cells to suppress the growth of tumors, or to suppress the proliferation of tumor cells. The present invention provides such a use for placental stem cells and populations of the same.